A wellbore simulator for mud-shale interaction studies

Abstract

A wellbore simulator for investigating mud/shale interactions is described. Outcrop Pierre Shale is prepared for test by an initial drainage stage, in order to reduce the chemical potential of the pore water to a value more representative of buried rock. This enhances swelling when the shale is subsequently placed in contact with deionised water. Unlike vapour phase equilibration of chemical potentials, the stresses applied during drainage compact the shale. This is thought to destroy some of the cementation within the shale, though to nowhere near the extent that occurs when shales are reconstituted from ground material. The wellbore radius is measured during swelling by means of a caliper, and results obtained using several drilling muds are reported in order to demonstrate the shale to stresses applied during drainage is analyzed using poroelacticity theory, assuming isotropy of the shale. This leads to estimates of the shale mechanical properties which are in line with literature values.